Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2. Most thermostatic expansion valves are set for a superheat of

20°C

5°C

10°C

15°C

3. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

4. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Sub-cooling or under-cooling

Normal cooling

Super-cooling

5. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

Superheat the vapour

6. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

7. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

Capillary tubes

8. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

None of these

Positive

Negative

9. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Carnot

Rankine

10. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

12. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

13. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

14. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

15. A bootstrap air cooling system has

Four heat exchangers

Two heat exchangers

Three heat exchangers

One heat exchanger

16. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

All of these

Domestic refrigerators

17. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

40 tons

0.1 ton

18. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

19. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

30 bar

8 bar

15 bar

20. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

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21. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Bell Coleman

Carnot

22. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

23. In a lithium bromide absorption refrigeration system

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

24. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

25. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

2.33

4.33

3.33

26. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

27. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

28. Freon group of refrigerants are

Inflammable

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

29. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 1

1: 9

1: 3

30. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.6

0.67

0.4

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31. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

32. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Freon

Carbon dioxide

Brine

33. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Absorber

Condenser

34. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

35. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Axial

Piston type reciprocating

36. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Always less than unity

Equal to unity

37. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

High risibility with oil

Good electrical conductor

38. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-75.2°C

-77.7°C

39. For obtaining high COP, the pressure range of compressor should be

Optimum

Low

Any value

High

40. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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